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Edoardo Pozio

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date: 26 January 2022

Trichinellosis is caused by nematodes of the genus Trichinella. These zoonotic parasites show a cosmopolitan distribution in all the continents, but Antarctica. They circulate in nature by synanthropic-domestic and sylvatic cycles. Today, eight species and four genotypes are recognized, all of which infect mammals, including humans, one species also infects birds, and two other species infect also reptiles.

Parasites of the genus Trichinella are unusual among the other nematodes in that the worm undergoes a complete developmental cycle, from larva to adult to larva, in the body of a single host, which has a profound influence on the epidemiology of trichinellosis. When the cycle is complete, the muscles of the infected animal contain a reservoir of larvae, capable of long-term survival. Humans and other hosts become infected by ingesting muscle tissuescontaining viable larvae.

The symptoms associated with trichinellosis vary with the severity of infection, i.e. the number of viable larvae ingested, and the time after infection. The capacity of the worm population to undergo massive multiplication in the body is a major determinant. Progression of disease follows the biological development of the parasite. Symptoms are associated first with the gastrointestinal tract, as the worms invade and establish in the small intestine, become more general as the body responds immunologically, and finally focus on the muscles as the larvae penetrate the muscle cells and develop there. Although Trichinella worms cause pathological changes directly by mechanical damage, most of the clinical features of trichinellosis are immunopathological in origin and can be related to the capacity of the parasite to induce allergic responses.

The main source of human infection is raw or under-cooked meat products from pig, wild boar, bear, walrus, and horses, but meat products from other animals have been implicated. In humans, the diagnosis of infection is made by immunological tests or by direct examination of muscle biopsies using microscopy or by recovery of larvae after artificial digestion. Treatment requires both the use of anthelmintic drugs to kill the parasite itself and symptomatic treatment to minimize inflammatory responses.

Both pre-slaughter prevention and post-slaughter control can be used to prevent Trichinella infections in animals. The first involves pig management control as well as continuous surveillance programmes. Meat inspection is a successful post-slaughter strategy. However, a continuous consumer education is of great importance in countries where meat inspection is not mandatory.

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